In a typical liquid crystal display (LCD) device, light emitting diodes (LEDs) are used as backlight sources. A plurality of LEDs are connected in series to form an LED lightbar. Then, the LED lightbar is driven by a special power management module to illuminate. The power management module includes a power management chip. Some power management chips have a pulse width modulation (PWM) dimming function, namely the power management chips can control brightness of the LED lightbar by controlling an effective current value of the LED lightbar. However, some power management chips do not have the PWM dimming function, resulting in that the power management chips and dimming function may not be simultaneously achieved.